Wave length modulation



' gr I CORRECTED 400/0 FREQUENCY 11, 1942. M. CROSBY 2,292,868

WAVE LENGTH MODULATION Original Filed March 9, 1940 c camcr/au FOROl/fPl/T MM! 3 FM RECEIVER RFCE/VE'R & RFC'f/Vl/VG RECEIVING g PM WA lFs PM WAVES 400/0 FRt-Q. AUDIO FRE i F a L l 7; Fl/IJR .9 3 muss FREQFREQUENCY M455 1 M00UL4TE0 M00. uooumr/a/v 4400024270 J] WAVE EC-TRANSMITTER RECEIVER PHASE Mom/M270 FFc Fu/ R 70 F/ .4 PHASE yA/mo. m:(/58 If I20 1 6 FREQ.

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/J; FM/2 FREQUENCY T ll MOOULAIEO I x t OY/VJTRO/V OSCILLATOR i I IREC-(7V5 OSC/L LATOR INVENTOR MURRAY 6. CROSBY ATTORNEY Patented Aug.11, 1942 2,292,866 WAVE LENGTH MODULATION Murray G. Crosby, Itiverhea'd,N. Y., assignor to Radio Corporation of America,

of Delaware a corporation Application March 9, -194,0, Serial No.323,077, which is a division of application Serial No. 618,154, June 20,1-932. 'Divided and this application November 27, 1940, Serial No.367,308

Claims. gor. 250-2028) This application concerns wave length modulationsignalling means and methods and is a division of my United Statesapplication #323,077 filed March 9, 1940, now U. S. Patent No. 2,230,-

212, dated January 28, 1941, the latter application, in turn, being adivision of my U. S. application #618,154 filed June 20, 1932, now U. S.Patent No. 2,229,640, dated January 28, 1941.

In describing my invention, reference will be made to the attacheddrawing wherein:

Figs. 1 and 2 are curves used in illustrating the principle involved inmy method and means; while,

Figs. 3 and 4 are respectively adiagrammatical and a somewhat detailedshowing of a. wave length modulated wave translating means arranged inaccordance with my invention;

As pointed out in detailhereinafter and in my two parent cases referredto above, if phase modulated wave energy is impressed on a frequencymodulated wave receiver, the receiver output, 1. e., the variations atsignal frequency is not truly representative of the original modulatingwave, but is modified as to amplitude substantially in proportion to itsfrequency. Thus, the

lower modulation frequencies in the output are relatively attenuated asshown, for example, by the line A of Fig. 1. An output, as representedby the dotted line B of Fig. 1, is desired. In the said prior cases,means in the form of a correction network responsive to modulationfrequencies and having a characteristic such as shown by the curve C ofFig. 2 is provided in the output of the receiver to additionally modifythe modulating potentials from the detector in a sense to cure theprevious described distortion. Thus, the overall effect is correct andis as indicated by curve B of Fig. 1.

In Figs S and 4 has been shown an arrange- 'ment in which, by means of anovel circuit, a

corrective effect, which is the converse of the manner in which phasemodulatedsignals are widely separated points.

in sequence, the distortion effects, which are the inverse of eachother, will add or cooperate to give a resultant signal which is trulyrepresentative of the initial signal to be worked with. This might seemlike a devious route to follow to receivephase modulation. Actually, itis'not, however, 'and is, on the contrary, a convenient manner toreceivephas' e modulated signals under certain conditions. The phasemodulated signals are first received on a frequency modulated receiver,then converted by means of a local modulating means (transmitter) tofrequency modulation, and received on a phase modulation receiver asshown in Fig. 3.

The logical assumption may be that, since a phase modulated signalreceiver is used'in this correction circuit, the phase modulationsshould be received directly on that unit. However,

there are reasons for following the present course. First, the receivedsignal output from phase modulated signals received on' a frequencyreceiver, including correcting means is different from that receiveddirectly on a-phase modulation receiver with respect to interference,fading, and tuning characteristics. corrected frequency modulationreceiver (receiving phase modulated signals) will feed a certain circuitmore suitably than a phase modulation receiver receiving the samesignals directly. Second, the phase modulation system, including thelocal frequency modulation transmitter, when used for'acorrectio'ncircuit, in accordance with the present invention, is far moresimplified than when the transmitter and receiver are at by aninspection of the circuit of Fig. 4, which shows a correction circuit ofthis type in detail.

In Fig. 4, the signal frequencies to be corrected are applied from thedetector of the frequency modulation receiver FMR tuned to and receivingthe phasemodulated signal picked up by the antenna to the inputterminals of a transformer 50. The secondary winding of transformer is"connected to the control electrode 9!) of an oscillation generator SIof the dynatron type. The anode 92 is connected with an oscillatorycircuit 93 in which oscillations at high frequency are developed byproducing a negative resistance e'fiect'in the anode cathode circuit, asdisclosed more in detail in United States application Ser. No. 608,383,filed April 30, 1932, now Patent #2,085,739, issued July 6, 1937. Thehigh frequencies generated by the dynatron oscillator are modulated infrequency, as disclosed more in detail in the above identifiedapplication. The

Consequently, a x

This may be realized modulated oscillations are impressed from thecircuit 93 on to a winding 94, and from winding 94 in opposition to thecontrol electrodes 95 and 96 of thermionic differential detectors 98 andI of a phase modulation receiver. The anodes IOI and I02 of differentialdetectors 98 and I00 are connected in series through resistances H0 andI II, as shown. Charging potential for the anodes is supplied from asource I03 connected between the terminals of resistances H0 and III andthe cathodes of tubes 98 and I00. The different currents resulting fromthe signal frequencies impressed oppositely to the control electrodes oftubes 98 and I00 flow in the resistances H0 and II I. These differentcurrents are applied from the high potential terminals of resistances H0and I II to the input terminals of a radio filter circuit comprisingseries inductances I and I and parallel condensers C4 connected asindicated. After passing through the filter circuits I, I, C4, thedifierent currents flow through resistances R5, R6 to the controlelectrode I05 and cathode I05 of a second dynatron oscillation generatorI08. Capacities C5 are connected between the terminals of theresistances R5, R6 and ground. These resistances and capacities regulateand determine the time constant of the circuit interposed between thedifferential resistors IIO, II I and the input electrodes of theoscillation generator I08 to regulate the sensitivity and rapidity ofthe control effect of the different currents on the oscillator I08.

A source I09 supplies direct current biasing potential to the gridelectrode of tube I08. The differential currents from resistances l I 8and III are superposed on this direct current potential. The outputcircuit II2 of the dynatron oscillation generator and modulator I08 iscoupled through a link circuit II 3 with a transformer I I4, thesecondary winding I I5 of which is connected in series with the controlelectrodes 95 and 96 of differential detectors 98 and I00 so that thecarrier frequencies developed in I I2 and modulated by the differentialcurrents in I08 are applied cophasally to the control electrodes of thedifferential detectors 98 and I00. This entire arrangement of thedifferential detectors and the frequency control means for thesupplemental modulator and generator I08 is, in many respects, similarto the automatic frequency control'device disclosed in United Statesapplication Ser. No. 616,803, filed June 13, 1932, now Patent#2,065,565, issued on December 29, 1936.

The detected signals appearing in the anodes of differential detectors98 and I00 are applied by way of coupling condensers H6 and II! to theterminals of series resistances H8, H9 and from the terminals of saidresistances to the control electrodes of a pair of amplifier tubes I20and I2I having their anodes connected through the primary winding 63' ofa transformer 64'. This phase modulation receiver, including thedifferential detectors 98 and I00, the frequency control means I08, andthe repeaters I20 and I 2|, impart to the modulated signals fromfrequency modulated dynatron 90, a distortion which is the converse ofthe distortion given to the initially received phase modulated signal bythe frequency modulation receiver FMR. The two distortion effects add toprovide in the output of transformer 64' a signal which is trulyrepresentative of the signal impressed on the original phase modulatedWave. The corrected signal frequencies may be utilized from thesecondary winding 65 of this transformer.

What is claimed is:

1. The method which includes subjecting a phase modulated wave to afrequency demodulation, frequency modulating a carrier wave with thedemodulated wave and subjecting the frequency modulated wave to a phasedemodulation.

2. In combination, means producing phase modulated waves, meanssubjecting the phase modulated waves to a frequency demodulation, meansfor frequency modulating a carrier with the demodulated waves and meansfor passing the frequency modulated carrier through a phase demodulatingsystem.

3. Means for demodulating a wave modulated in phase comprising incombination a demodulation system which when energized by phasemodulated waves produces an audio frequency output the amplitude ofwhich varies substantially directly as the frequency of the signalmodulations on the phase modulated wave, means for impressing said waveon said demodulator, an oscillatory circuit in which oscillatory waveenergy may be caused to flow, means coupling said oscillatory circuit tosaid demodulator to frequency modulate the oscillatory energy flowing insaid circuit, a wave demodulator which when energized by frequencymodulated waves produces an audio frequency output the amplitude ofwhich varies substantially inversely as the frequency of the modulationson the frequency modulated wave, means coupling said last nameddemodulator to said oscillatory circuit, and a signal utilizing meanscoupled to the output of said last named demodulator.

4. A correction circuit for adapting a frequency modulation receiver tothe reception of phase modulated waves which includes, a tube having anoscillation circuit and a circuit for applying signals from saidfrequency modulation receiver to said tube to modulate in frequency theoscillations in said circuit, and a phase modulated signal demodulatorof the thermionic type coupled to said tube.

5. A correction circuit for adapting a frequency modulated wave receiverto the reception of phase modulated waves which includes, a thermionictube having an oscillation circuit and a circuit for applying signalsfrom said frequency modulated wave receiver to said tube to modulate infrequency the oscillations in said circuit, and a phase modulated signaldemodulator of the thermionic type coupled to said first tube, saiddemodulator being of the automatic frequency control type.

6. In signalling apparatus the combination of a demodulator normallyresponsive to waves modulated in frequency in accordance with signals,means for impressing waves modulated in phase in accordance with signalson said demodulator to obtain therefrom signals inherently distorted bysaid demodulator, a frequency modulator comprising a signal input and anoscillatory circuit, means for impressing said distorted signals fromsaid demodulator on the signal input of said frequency modulator, and ademodulator normally responsive to waves modulated in phase inaccordance with signals coupled to said oscillatory circuit wherebyfrequency modulated energy from said oscillator circuit of saidfrequency modulator is impressed on said last named demodulator toobtain therefrom resultant signals inherently distorted by saiddemodulator in a sense opposite to the distortion of the signal by saidfirst demodulator to thereby obtain non-distorted signal demodulation ofsaid wave.

7. A signalling system including, a source of wave energy the phase ofwhich is modulated in accordance with signals, a frequency modulatedwave demodulator excited by energy from said source, a wave sourcecoupled to said demodulator and controlled as to frequency of operationthereby and wave translating means excited by controlled wave energyfrom said wave source.

8. The method of signalling with a source of wave energy the phase ofwhich is modulated in accordance with modulating potentials whichincludes the steps of, subjecting said phase modulated wave energy fromsaid source to a frequency demodulation, modulating the frequency of acarrier wave in accordance with the demodulated wave energy andtranslating the said carrier wave so modulated.

9. In a signalling system in combination, a source of wave energymodulated in phase in accordance with modulating potentials, a frequencymodulated wave demodulator excited by phase modulated waves from saidsource, a carrier wave frequency modulator excited by demodulated energyprovided by said demodulator, a tunable phase modulated wave demodulatorexcited by modulated carrier wave from said modulator, and means excitedby currents derived from said last named demodulator to control the tunethereof.

10. A correction circuit for adapting a frequency modulated wavereceiver to the reception of phase modulated waves which includes, anelectron discharge tube having an oscillation circuit and a circuit forapplying signals from said frequency modulated Wave receiver to saidtube to modulate in frequency the oscillations in said circuit, and aphase modulated signal demodulator of the electron discharge tube typecoupled to said first tube.

MURRAY G. CROSBY.

